The present invention relates to a method of and an apparatus (laser radar) for detecting the shape and azimuth of and the distance to an object by use of laser light, and more particularly to a method and apparatus in which a desired detection ability can be obtained irrespective of any change of meteorological conditions.
In the conventional laser radar disclosed by JP-A-50-137762, a pencil beam is transmitted during a time when a target is caught and a fan beam which is divergent in a vertical direction is transmitted when the laser beam is out of the target range while the pencil beam is transmitted again when the target is acquired again.
In the above-mentioned conventional laser radar in which two kinds of laser beams having different divergence angles are used, the beam divergence angle is changed paying attention to only the capture of the target while the attenuation of laser light in the atmosphere is not taken into consideration. Since the rate of attenuation of laser light in the atmosphere changes depending on meteorological conditions, there arises a problem that a distance to a target which can be detected by a laser beam, that is, a detectable distance may be different even when the detection of the target is made with the same beam divergence angle.